mask or obscure a object on video

I can’t find a proper solution to let the lightstreaks and particles pass the backside of the clock. I have a mask setup to obscure the truss in the foreground and I’ve setup a plane and tracked it to the clock in order to obscure the light when it passes the clock at the back. But I cannot come up with a solution that works. Anyone?

kind regards,

You can use a stand-in proxy object that imitates the clock to mask the particles and streak. Position it so that it matches the outline of the real clock and is in correct place depth wise. Put it onto its own layer and use that layer as a mask in render layer setup. This will “cut” a hole into streak and particles when they are behind the clock.